Abstract

The actinic (i.e., photolysis) wavelength dependence of chlorine dioxide (OClO) photochemistry in solution is investigated. Femtosecond pump–probe studies performed with 355-nm photoexcitation are presented for OClO dissolved in water and acetonitrile. Relative to earlier studies employing 400-nm photoexcitation, a decrease in primary-photoproduct geminate-recombination efficiency is observed in both solvents. This decrease in recombination efficiency is especially dramatic in acetonitrile where the recombination quantum yield is found to be only 0.08±0.04. The solvent and actinic-wavelength dependence of geminate recombination is discussed with respect to the recent theoretical work of Benjamin and co-workers [J. Chem. Phys. 116, 8930 (2002)]. Substantial increases in the optical density at 267 nm are also observed that cannot be explained by considering the increase in ClO concentration accompanying a reduction in geminate-recombination efficiency exclusively. Instead, these increases are consistent with an increase in the quantum yield for ClOO and/or Cl production suggesting that the partitioning between OClO photoproduct channels is actinic-wavelength dependent.